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HS8.3.2

Modeling soil and vadose zone processes is vital for estimating physical states, parameters and fluxes from the bedrock to the atmosphere. While the media soil, air and water physically affect biogeochemical processes, transport of nutrients and pollutants, and infiltration-runoff generation, the implications on ecosystem functions and services and terrestrial storage capacities are vital to the understanding of global, land use and climate change. Advanced measurement techniques, increased availability of high-frequency models and data, and the need for terrestrial system understanding challenge vadoze zone modeling concepts, budging model parameterizations from static to near dynamic. This session aims to bring together scientists advancing the current status in modelling soil processes from the pore to the catchment and continental scale. We welcome contributions with a specific focus on soil hydrological processes but also those that address the role of soil structure on land surface processes, soil biogeochemical processes and their interactions with hydrology, transport of pollutants, and soil vegetation atmosphere modelling.

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Co-organized by SSS10
Convener: Roland BaatzECSECS | Co-conveners: Stefano Barontini, Amro NegmECSECS, Martine van der Ploeg, Harry Vereecken
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| Attendance Wed, 06 May, 14:00–15:45 (CEST)

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Chat time: Wednesday, 6 May 2020, 14:00–15:45

Chairperson: Stefano Barontini, Roland Baatz, Martine van der Ploeg
D371 |
EGU2020-5507
Peter Finke, Nirmani Ranathunga, Ann Verdoodt, Yanyan Yu, and Qiuzhen Yin

Loess deposits often contain paleosols that are documenting phases of soil formation associated with interglacials or interstadials. Linkage of the paleosols to paleoclimates is not straightforward when paleoclimates are represented by dynamic (simulated) variables and paleosols by static (measured) soil parameters. We therefore propose to combine a dynamic soil model with a climate model. We define the required processes in such soil model and the output variables that would allow usage of the soil-climate model combination to be used for (past and future) climate change studies. Issues to be considered are the time- and spatial scale of the soil and the climate model. For predictive (global change) studies, the usage of (soil) model outputs to quantify the evolution of the soil natural capital and of ecosystem services must be considered. We give examples for the Chinese Loess Plateau of the evaluation of paleoclimate-paleosol linkages and of simulated soil natural capital and soil ecosystem services with the LOVECLIM-earth system model linked to the SoilGen soil evolution model and conclude that such model combination is an important step forward.

How to cite: Finke, P., Ranathunga, N., Verdoodt, A., Yu, Y., and Yin, Q.: Evaluating paleoclimate-paleosoil linkages and soil ecosystem services with a combined soil-climate model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5507, https://doi.org/10.5194/egusphere-egu2020-5507, 2020.

D372 |
EGU2020-4368
Jiaxin Wang, Xining Zhao, and Xiaodong Gao

Vapor flow plays major role in soil–atmosphere water exchange in arid regions, and can be partly driven by airflow, but its impact is often neglected. In this study, a two-year field experiment was conducted in a dry agricultural region on the Tibet Plateau (TP) to investigate the effect of airflow on soil hydro–thermal dynamics and evapotranspiration modeling under three cultivation patterns: ridge-furrow planting with black-film mulching (RM), flat planting with black-film mulching (FM), and flat planting with no mulching (FN). An airflow-incorporated, based on Philip and de Vries (PdV) model, STEMMUS (Simultaneous Transfer of Energy, Mass and Momentum in Unsaturated Soil) was adopted. Considering objective’s (Lycium barbarum L.) sparse canopy, excluding Penman-Monteith (P-M) algorithm which already employed in STEMMUS, Shuttleworth-Wallace (S-W) model was incorporated into STEMMUS model to simulate evapotranspiration rate. Validation results showed that STEMMUS reliably captured the behaviors of observed soil moisture, soil temperature, and evapotranspiration (index of agreement d = 0.4, 0.6 and 0.5 for soil moisture under FN, FM and RM; 0.9 for soil temperature under three treatments; 0.6, 0.6 and 0.8 for evapotranspiration under FN, FM and RM; 0.6, 0.5 and 0.5 for evaporation under FN, FM and RM). Incorporating airflow extended the 0-1 m soil profile temperature modeling precision (d value improved 1%), led to the maximum 5% gap of soil moisture at 20 cm depth, and 3.7 mm d-1 gap of daily evapotranspiration compared to pattern without airflow under non-mulched treatment. However, the impacts of airflow are weak under mulching treatments (the gaps between including/excluding airflow modeling were within 0.1% for soil moisture, 0.1 ℃ for soil temperature and 0.1 mm d-1 for evapotranspiration). Furthermore, the effect of coupling airflow became significant when water inputs (precipitation/irrigation) were higher than 18 mm. Incorporating S-W model successfully improved evapotranspiration modeling precision, with d values increased by 0.5% and 1% for FM and FN respectively in evapotranspiration simulation, increased by 0.5%, 6.4% and 2.2% for RM, FM and FN respectively in evaporation simulation. The results here provide insights into the role of airflow in soil hydrology modeling in arid and semi-arid regions.

How to cite: Wang, J., Zhao, X., and Gao, X.: Soil hydrology and crop evapotranspiration modeling in a dry agricultural region of the Tibet Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4368, https://doi.org/10.5194/egusphere-egu2020-4368, 2020.

D373 |
EGU2020-19210
Lisa Bahlmann, Insa Neuweiler, Kathleen Smits, Katharina Heck, Edward Coltman, and Rainer Helmig

Transport of gas components in the unsaturated zone and across the soil surface plays a role for transport of volatile contaminants, gases from pipe leaks or greenhouse gases. When estimating flow rates from the soil into the atmosphere, a good understanding of the transport processes is important. In general, component transport in the gas phase is considered to be mainly due to diffusion. However, the wind field above the soil surface can induce flow into the subsurface and influence transport and mass fluxes.

We present a study on gas component transport through dry and partially saturated soil into a free air flow above the soil surface, considering gas components of different density. Laboratory experiments in a quasi-2d sand tank were carried out. The tank was placed underneath a wind tunnel, and different wind velocities were used. Gases with different densities were injected with constant rate at an inlet port. Concentration distributions were measured continuously with sensors that were installed inside of the tank. After establishing a steady state concentration distribution, the gas injection was stopped and the decrease of gas concentrations inside the tank was monitored.

The experiments show that the concentration profiles under steady state gas injection depend on gas density and the different diffusion coefficients. They depend only slightly on the velocity of the overlaying wind field and the influence is mainly seen very close to the soil surface. The transient gas transport out of the soil, however, did not only depend on the different diffusion coefficients, but was clearly influenced by the wind field. The transient 2d concentration distribution fields illustrate that the wind field induced a flow field inside the tank that depends on the wind velocity and the component density and influences the gas component transport. The influence increases under partly saturated conditions.

To reproduce the transport correctly, it is necessary to capture the coupling between free flow and porous medium flow and the transport in the coupled flow. To do so, we use a fully coupled flow and transport model implemented into the environment DuMux ((Dune for Multi-(Phase,Component, Scale, ...) flow and transport in porous media). It can be shown that including the coupling concept, the main features of the concentration distributions can be reproduced for both the steady state and the transient case. With the model it is also demonstrated, that although advective fluxes inside the porous medium introduced by the wind field (horizontal and lateral) are relatively small in comparison to the diffusive fluxes, they cause relevant changes in the concentration distribution and thus indirectly influence the mass fluxes inside the porous medium and across the soil-atmosphere interface.

How to cite: Bahlmann, L., Neuweiler, I., Smits, K., Heck, K., Coltman, E., and Helmig, R.: Transport of gas components across the soil – atmosphere interface influenced by wind conditions: A study with laboratory experiments and coupled subsurface – free flow modelling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19210, https://doi.org/10.5194/egusphere-egu2020-19210, 2020.

D374 |
EGU2020-6537
Shmuel Assouline and Tamir Kamai

Accurate estimates of water losses from the soil by evaporation are important for hydrological, agricultural, and climatic purposes. Different analytical and numerical approaches were developed to provide the capability to simulate and predict the dynamics of the evaporation process in terms of fluxes, and water and thermal distributions in the soil profile. Experimental investigation of the process under different boundary conditions is also possible by means of columns and weighing lysimeters. As part, these experimental setups allow addressing the impact of heterogeneity in the drying soil profile. Experimental data resulting from evaporation experiments under natural and laboratory conditions with homogeneous and heterogeneous soil profiles are presented and analyzed. These data are also compared to results from available analytical and numerical models. This comparison points out fundamental limitations of the approaches that assume hydraulic connectivity up to the surface, as well as those that suppose monotonic drying when unsteady conditions prevail. Differences between experimental data and model prediction emphasize challenging knowledge gaps that are part of ongoing research.

How to cite: Assouline, S. and Kamai, T.: Evaporation from homogeneous and heterogeneous soil systems: Modeling approaches and experimental data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6537, https://doi.org/10.5194/egusphere-egu2020-6537, 2020.

D375 |
EGU2020-18501
Jannis Groh and the crop-soil modelling initiative

Agro-ecosystem models have been developed to study effects of agricultural management on crop production, mostly from an agronomic point of view. Based on a biophysical process representation, their most prominent advantage is the coupled modelling of crop development and yield formation, as well as water and nutrients fluxes in the plant-soil system. Crop models have previously been calibrated based on experimental data with a focus on plant observations. Less attention has been given to soil water and solute dynamics despite the importance of plant nutrient availability and chemical leaching, particularly for arable soils often affected by erosion. The question was whether the description of soil processes and properties play an important role in the crop simulations.

The aim of this study was to compare the ability of agro-ecosystem models to predict crop development and water fluxes under changing environmental conditions. Observations on crop growth and soil water dynamics were obtained from four weighable lysimeter of the TERENO-SOILCan lysimeter network in the northeast of Germany (Dedelow). The intact soil monoliths are representative for the spatial soil variability of erosion-affected hummocky agricultural landscape. Twelve agro-ecosystem models (AgroC; DailyDayCent; Daisy; HERMES; MONICA; Theseus, Theseus-HydroGeoSphere; Theseus-Hydrus-1D; Expert-N coupled to CERES, GECROS, SPASS, and SUCROS) were tested. Crop development stages were used to calibrate the agro-ecosystem models. The model performance was tested against observed grain yield, aboveground biomass, leaf area index, actual evapotranspiration, drainage, and soil water content.

Model descriptions were highly diverse for both crop development and water fluxes. Crop growth and soil water fluxes were better predicted by the Multi Model Mean simulations than by any individual model. Results demonstrate that i) the hydraulic properties of erosion-affected soil profiles controlled the observed interactions between crop yield, plant development, and water fluxes, ii) data on phenological stages contained insufficient information content to calibrated agro-ecosystem models for soils affected by erosion, and iii) neither an individual model nor the Multi Model Mean could describe the observation on crop development and water dynamics, when using phenological stages only for model calibration. The results suggest that soil does matter in agro-ecosystem models and that weighable lysimeter can provide such soil related observation.

How to cite: Groh, J. and the crop-soil modelling initiative: Crop growth and soil water fluxes at erosion-affected arable sites: A model inter-comparison based on weighing-lysimeter observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18501, https://doi.org/10.5194/egusphere-egu2020-18501, 2020.

D376 |
EGU2020-9894
Edoardo Martini, Ute Wollschläger, Marco Bittelli, Fausto Tomei, Ulrike Werban, Steffen Zacharias, and Kurt Roth

As most hydrological processes are highly nonlinear and controlled by time-varying boundary conditions, numerical models are required for their comprehensive representation. However, one of the major difficulties in vadose zone processes modeling is due to the fact that soils are heterogeneous at all spatial scales. The identification and accurate representation of such heterogeneity can be crucial for quantifying the subsurface hydrological states and water fluxes but it is still a challenge in soil hydrology.

We present an integrated approach for process-based modeling of the vadose zone for a typical hillslope. The approach builds on the integration of classical soil mapping, on accurate monitoring of soil water content as well as on geophysical measurements for characterizing the subsurface heterogeneity. It finally integrates the gathered information into a physical model for simulating the vadose-zone processes with high spatial and temporal resolution.

Starting with a simple soil representation, we present the modeling results for different scenarios of increasing complexity with focus on the discretization and corresponding hydrological parameterization of the soil structures in three dimensions. We highlight and discuss the key challenges that need to be addressed when continuous information about the subsurface heterogeneity is to be mapped in the field and represented in a numerical model.

We argue that linking state-of-the-art experimental methods to advanced numerical tools, and bridging the gap between different disciplines such as pedology, hydrology and geophysics can be the key for improving our ability to measure, predict and better understand the vadose-zone processes. This will provide important knowledge needed for transferring this approach to larger scales where the accurate quantification of the soil water fluxes is required for a more efficient water management in the context of sustainable food production and climate change.

How to cite: Martini, E., Wollschläger, U., Bittelli, M., Tomei, F., Werban, U., Zacharias, S., and Roth, K.: Process-based hydrological modeling: accounting for subsurface heterogeneity by integrating pedology, geophysics and soil hydrology, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9894, https://doi.org/10.5194/egusphere-egu2020-9894, 2020.

D377 |
EGU2020-21673
Martin Bouda, Jan Vanderborght, Valentin Couvreur, Félicien Meunier, and Mathieu Javaux

Estimating plant uptake of soil water has been a persistent problem in process-based earth system models (ESMs). Initially ignored altogether, plant access to soil water was long modelled with heuristic approaches at large scales. These formulations are currently being replaced as ESMs begin to incorporate more detailed plant hydraulics schemes based on the soil-plant-atmosphere continuum concept. While the new schemes greatly improve mechanistic description of above-ground plant hydraulics, they have given rise to various issues belowground, from excessive hydraulic redistribution to numerical instability. As detailed 3D descriptions of root systems and water flow equations on the soil-root domain have been established, the key challenge is how to scale them up to relevant scales, reducing computational cost to a trivial level without loss of accuracy.

Here, we set out a mathematical framework that incorporates recent advances in this area and allows us to relate them to each other. Comparing and contrasting different models, formulated in a novel matrix form of the water flow problem in the root system, allows us to make inferences about their suitability for use in upscaling. We are able to show how to avoid discretization error in the upscaled root scheme, as well as which upscaling method offers full generality, and which yields the computationally simplest forms. These theoretical results are fully supported by numerical simulations of fully explicit 3D root systems and their upscaled versions. Improved performance of the upscaled models is also demonstrated in an application to field data from the Wind River Crane flux tower site (reduced model bias, root mean squared error, and increased robustness of fitted parameters).

Root water uptake equations can now be scaled up without discretization error for arbitrary root systems. The chief remaining source of error is soil moisture heterogeneity within discretized soil elements where it is assumed uniform by any given model (e.g. within each vertical layer). The main task for future work thus becomes to achieve a correspondingly accurate description for soil moisture heterogeneity. Some of the upscaling approaches compared here offer hints at potential next steps in this direction.

How to cite: Bouda, M., Vanderborght, J., Couvreur, V., Meunier, F., and Javaux, M.: How to scale root water uptake from root scale to stands and beyond – a theoretical framework, practical lessons, and next steps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21673, https://doi.org/10.5194/egusphere-egu2020-21673, 2020.

D378 |
EGU2020-1470
Zhaoyang Luo, Jun Kong, Zhiling Ji, Chengji Shen, Chunhui Lu, Pei Xin, Zhongwei Zhao, Ling Li, and D. Andrew Barry

The soil water retention curve (WRC), describing the relation between the soil water content and its corresponding capillary pressure, relies not only on whether drying or wetting occurs but also on the pore scale water flow velocity. Here, we investigated the effects of the watertable fluctuations on the WRC through 28 laboratory experiments covering a wide range of fluctuation amplitudes and periods. Results show that both the response of the capillary pressure and soil water content lag behind the watertable fluctuation, and the vertical capillary pressure distribution in the unsaturated zone is non-hydrostatic, especially for the fluctuations with shorter period. As a consequence of watertable fluctuation, the measured WRC deviates from that under static conditions, depending on both the fluctuation amplitude and period. Moreover, the air-entry pressure under dynamic conditions is considerably larger than that under static conditions, and it first increases and then decreases as the fluctuation period decreases. The effects of the watertable fluctuations on the dynamic capillary coefficient was further examined. It is found that the relation between the dynamic capillary coefficient and saturation is nonunique even for the drying and wetting of a given sand and watertable fluctuation, suggesting a hysteretic dynamic capillary coefficient, and the dynamic capillary coefficient is rate-dependent, decreasing with an increase of fluctuation rate.

How to cite: Luo, Z., Kong, J., Ji, Z., Shen, C., Lu, C., Xin, P., Zhao, Z., Li, L., and Barry, D. A.: Watertable fluctuation-induced variability in the water retention curve: Sand column experiments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1470, https://doi.org/10.5194/egusphere-egu2020-1470, 2019.

D379 |
EGU2020-3716
Quirijn de Jong van Lier and Everton Alves Rodrigues Pinheiro

Vadose zone hydrological models employing finite difference numerical solutions of the Richards equation allow simulating the movement and predicting the state of soil water and associated quantities in the vadose zone. Nowadays, robust algorithms like Hydrus and SWAP are available to perform such simulations. Since most numerical issues with these algorithms have been solved, hydraulic parameters describing the relation between conductivity K, pressure head h and water content θ determine the quality of model output. Whichever method is used to obtain soil hydraulic properties, resulting parameters include an uncertainty, which may be expressed as a confidence interval. Existing correlations between parameters may be expressed in a correlation matrix. Using a stochastic approach, uncertainty and correlation may be considered in simulations and their propagation in results can be assessed. We developed a software which generates n stochastic realizations of the hydraulic parameter set considering uncertainty (standard error) and correlation matrix, runs the SWAP model for each realization and extracts the model output of interest. To apply the software and assess the propagation of uncertainties in the model output, hydraulic properties were measured in soils from south-east Brazil using inverse modeling of laboratory evaporation experiments, resulting in Van Genuchten parameter values, respective errors and correlations. These data were used to obtain n (n=104) stochastic realizations of deep drainage, runoff and evaporation in a bare-soil scenario. Similarly, for a pasture cropped scenario the water balance components (including transpiration), and relative yield were evaluated. The effect of uncertainty in these parameters on the mentioned output variables prediction is presented and discussed.

How to cite: de Jong van Lier, Q. and Alves Rodrigues Pinheiro, E.: Uncertainty in soil hydraulic properties parameterization and its propagation in vadose zone hydrological model output , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3716, https://doi.org/10.5194/egusphere-egu2020-3716, 2020.

D380 |
EGU2020-3819
Marialaura Bancheri, Antonio Coppola, and Angelo Basile

Transfer functions are travel time probability density functions (TT pdfs), which describe the leaching behaviour in a given soil profile. Once they are defined, the output solute concentration at a given time and depth is simply the transfer function convolution with the input concentration signal to the system.

In this work we propose an extended version of Jury's transfer function model (TFM-ext). The proposed model allows to simulate the spatio-temporal distribution of nonpoint-source solutes along the unsaturated zone that: i) integrates a simplified statistical approach with the physically-based soil hydrological parameters; ii) is valid for wide range of applications, both in space and time; iii) is standard and easily replicable; iv) is easy to interpret.

With the assumptions of a) a gravity induced water flow, b) a conservative and nonreactive solute and c) a purely convective flow, ignoring the convective mixing of solute flowing at different velocities and the molecular diffusion, the TT pdf were calculated as functions of the unsaturated hydraulic conductivity k(θ). The strength of the model, despite its important assumptions, is that it derives the TT pdf from a physical quantity, i.e. the hydraulic conductivity function. Moreover, the model extends the transport process to the generic depth z, where information on the hydraulic properties could not be available, assuming a lognormal travel time pdf, whose parameters are scaled according to the generalized transfer function model.

A sensitivity analysis, based on Monte Carlo simulations, to evaluate to which parameters the TFM-ext is more sensitive, was performed. Results shown that θs and τ, of the van Genuchten-Mualem model, are the parameter affecting more the mean travel times.

Moreover, in order to validate TFM-ext, an application in the Telesina Valley, a hilly area of 200 km2 in Southern Italy, was performed. Forty-six soil profiles, completely characterized from the hydrological point of view, were used to evaluate the mean travel times and then compared with the results obtained with a notable physically based model, Hydrus 1D. Two distinct applications were performed: the first with constant upper boundary conditions equal to those applied to the TFM-ext exercise, and the second with real daily variable upper boundary conditions. Results of both cases gave very high correlation coefficients (above 0.8) and mean absolute errors of 30 and 40 days, respectively.

Eventually, the model was implemented as an operative tool for the groundwater vulnerability assessment within the geospatial Decision Support System developed for LANDSUPPORT H2020 project.

How to cite: Bancheri, M., Coppola, A., and Basile, A.: An extended transfer function model for the prediction of nonpoint-source pollutant travel times , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3819, https://doi.org/10.5194/egusphere-egu2020-3819, 2020.

D381 |
EGU2020-5718
Brivaldo Gomes de Almeida, Ceres Duarte Guedes Cabral de Almeida, Thaís Fernandes de Assunção, Bruno Campos Mantovanelli, José Coelho de Araújo Filho, and Giuseppe Provenzano

Soil management, although intended to create favorable structural conditions for crop growth and development, without prior assessment of potential and limitations, has been one of the reasons for the degradation of natural resources. The effects on soil degradation and respective structural quality are generally evaluated by some physical soil attributes such as bulk density (BD), total porosity (TP) and soil penetration resistance (PR). The PR is recognized as a physical parameter that supports the identification of areas with different stages of compaction and thus can be used to define appropriate management for soil remediation. Besides, this parameter depends on intrinsic soil factors (texture, structure, and mineralogy) and soil water content (SWC). Therefore, PR increases with BD and decreases with SWC (gravimetric or volumetric). Thus, it is possible to establish the critical limit of PR (PRCL) associated with the value of SWC that limits the growth of plant roots. PRCL varies according to soil type and plant species, but 2.0 MPa is the value scientifically accepted as the critical value to limit the root growth. Thus, the paper aimed to evaluate the spatial and temporal variability of PR in a field cultivated with sugarcane, under the conventional tillage system. The research was carried out in the Carpina Sugarcane Experimental Station, Pernambuco, Brazil. A grid of 70 x 70 m was delineated at intervals of 10 m and in each point soil samples were collected in the layers 0 - 0.30 m and 0.30 - 0.60 m depth. Three samplings were done to determine gravimetric soil water content; the first after six months of subsoiling (Time 6) before harrowing and planting, the second after 12 months of subsoiling (Time 12, six months after harrowing and planting) and the last after 18 months of subsoiling, before harvesting (Time 18). In each sampling time, in situ PR tests were carried out with the Solo Track equipment (Falker® - Model PLG 5300) and the simultaneous values of gravimetric soil water content were determined and associated with the PR data. The results showed that soil water content had a weak degree of spatial dependence, indicating the need to increase the number of samples. On the other hand, the PR values showed that the subsoiling did not promote a positive effect on the soil physical quality, with values above the PRCL for root development in Time 6 (2.42 MPa), even if after one year the sugarcane root system acted positively, by reducing PR in Time 18 (1.04 MPa) below the critical value.

How to cite: Gomes de Almeida, B., Duarte Guedes Cabral de Almeida, C., Fernandes de Assunção, T., Campos Mantovanelli, B., Coelho de Araújo Filho, J., and Provenzano, G.: Spatiotemporal variability of soil penetration resistance in a field cultivated with sugarcane under conventional tillage system in northeast Brazil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5718, https://doi.org/10.5194/egusphere-egu2020-5718, 2020.

D382 |
EGU2020-5787
Andreas Papritz, Peter Lehmann, Surya Gupta, Bonetti Sara, and Dani Or

The representation of land surface properties in hydrologic and climatic models critically depends on soil hydraulic functions (SHF). Parameters of SHF are routinely identified from soil water retention (SWR) and hydraulic conductivity (HC) data by nonlinear least squares. This is a notoriously difficult task because typically only few measurements are available per sample or plot for estimating the many SHF parameters (up to seven for the van Genuchten-Mualem model). As a consequence, the estimated parameters are often highly uncertain and could yield unrealistic predictions of related physical quantities such as the characteristic length Lc for stage‑1 evaporation (Lehmann et al., 2008). We address these limitations by capitalizing on the conditional linearity of some of the SHF parameters. Conditional linear parameters, say μ, can be substituted in the least squares objective by an explicit estimate (Bates & Watts, 1988), leading to an objective that depends only on the remaining nonlinear parameters ν. This step substantially reduces the dimensionality of the SHF estimation and improves the quality of estimated parameters. Additionally, instead of minimizing the least squares objective only with box constraints for ν, we minimize it by nonlinear programming algorithms that allow to physically constrain estimates of ν by Lc. We have implemented this estimation approach in an R software package capable of processing global SWR and HC data. Using ensemble machine learning algorithms, the novel parameter estimation results will be coupled with auxiliary covariates (vegetation, climate) to create improved global maps of SHF parameters.

References:

Bates, D. M. Watts, D. G. 1988. Nonlinear Regression Analysis and Its Applications. John Wiley & Sons, New York.

Lehmann, P., Assouline, S., Or, D. 2008. Characteristic lengths affecting evaporative drying of porous media. Physical Review E, 77, 056309, DOI 10.1103/PhysRevE.77.056309.

How to cite: Papritz, A., Lehmann, P., Gupta, S., Sara, B., and Or, D.: New solution to an old problem: improved parameter estimation of soil hydraulic functions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5787, https://doi.org/10.5194/egusphere-egu2020-5787, 2020.

D383 |
EGU2020-7004
Yixuan Xing, Rui Hu, Hongbiao Gu, Quan Liu, and Thomas Ptak

Under hydrostatic conditions, the water level observed in a well is often supposed to be equivalent to the pressure head in the surrounding aquifer. When the aquifer is subject to disturbing processes and activities, fluctuations of water level can be observed. Generally, the measured water level in the well is often considered to be less than the pressure head in the aquifer due to wellbore storage and skin effects (Ramey et al., 1972). In fact, there is another factor that can suppress or enhance the oscillating water level, which is termed the amplification effect (Cooper et al., 1965). Related studies point out that this effect is affected by well geometry (e.g. well diameter, water column height and well screen length), aquifer properties (e.g. transmissivity and storativity) and the period of the disturbed pressure head (Kipp, 1985; Liu, 1989). However, previous studies have obvious divergences in quantifying the amplification effect.

In this work, we firstly established an idealized fluid model to simplify the complex solid-fluid coupling process, aiming to discuss the influence of different well geometry parameters on the amplification factor separately, such as the well diameter, water column height and well screen length. Subsequently, we built a well-aquifer coupling numerical model to study the well-aquifer response induced by disturbed pressure based on the finite element method. Simulations of 125 scenarios showed that the amplification factor gradually increased until it reached a peak, and then decreased to 1 as the period of disturbed pressure became larger. The corresponding period of an amplification factor peak was significantly influenced by the water column height, which controlled the position of an “optimal period”. Aquifer properties can also affect the amplification factor, especially its peak value. In further numerical studies, more complicated scenarios will be investigated, considering different types of wells and aquifers.

How to cite: Xing, Y., Hu, R., Gu, H., Liu, Q., and Ptak, T.: A novel numerical modelling of well-aquifer response induced by pressure disturbance, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7004, https://doi.org/10.5194/egusphere-egu2020-7004, 2020.

D384 |
EGU2020-7172
Alexander Sternagel, Ralf Loritz, Wolfgang Wilcke, and Erwin Zehe

Recently, we proposed an alternative model concept to represent rainfall-driven soil water dynamics and especially preferential water flow and solute transport in the vadose zone. Our LAST-Model is based on a Lagrangian perspective on the movement of water particles (Zehe and Jackisch, 2016) carrying solute masses through the subsurface which is separated into a soil matrix domain and a preferential flow domain (Sternagel et al., 2019). The preferential flow domain relies on observable field data like the average number of macropores of a given diameter, their hydraulic properties and their vertical length distribution. These data may either be derived from field observations or by inverse modelling using tracer data. Parameterization of the soil matrix domain requires soil hydraulic functions which determine the parameters of the water particle movement and particularly the distribution of flow velocities in different pores sizes. Infiltration into the matrix and the macropores depends on their respective moisture state and subsequently macropores are gradually filled. Macropores and matrix interact through diffusive mixing of water and solutes between the two flow domains which again depends on their water content and matric potential at the considered depths.

The LAST-Model was evaluated using tracer profiles and macropore data obtained at four different study sites in the Weiherbach catchment in south Germany and additionally compared against simulations using HYDRUS 1-D as benchmark model. The results generally corroborated the feasibility of the model concept and particularly the implemented representation of macropore flow and macropore-matrix exchange. We thus concluded that the LAST-Model approach provides a useful and alternative framework for simulating rainfall-driven soil water and solute dynamics and fingerprints of preferential flow.

This study presents an extension of the model allowing for the simulation of reactive solute transport. Transformation kinetics are considered by transferring mass from the parent to the child components in each water particle according to the corresponding reaction rates, which is limited by the compound solubility. A retardation coefficient is not helpful in the particle-based framework, as the solute mass is carried by the water particles and travels thus by default at the same velocity. Ad- and desorption are explicit represented through transfer of dissolved mass from the water particles at a given depth to surrounding adsorption sites of the soil solid phase and vice versa. This may either operate under rate-limited or non-limited conditions. Adsorbed solute masses will be considered to be degraded following first-order reaction kinetics. The retardation process delays the solute displacement and enables a suitable time scale for the degradation process, which must be smaller than the time scale for the re-mobilization of the solutes. The proposed extension will be benchmarked against observations of pesticide transport in soil profiles and at tile-drained field sites.

 

Zehe, E., Jackisch, C.: A Lagrangian model for soil water dynamics during rainfall-driven conditions, Hydrol. Earth Syst. Sci., 20, 3511–3526, https://doi.org/10.5194/hess-20-3511-2016, 2016.

 

Sternagel, A., Loritz, R., Wilcke, W., and Zehe, E.: Simulating preferential soil water flow and tracer transport using the Lagrangian Soil Water and Solute Transport Model, Hydrol. Earth Syst. Sci., 23, 4249–4267, https://doi.org/10.5194/hess-23-4249-2019, 2019.

How to cite: Sternagel, A., Loritz, R., Wilcke, W., and Zehe, E.: Simulating preferential soil water flow and reactive solute transport using the Lagrangian Soil Water and Solute Transport Model (LAST), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7172, https://doi.org/10.5194/egusphere-egu2020-7172, 2020.

D385 |
EGU2020-7575
Boguslaw Usowicz and Jerzy Lipiec

Soil organic carbon accumulation is central to the improvement of many soil properties and functions. Biochar use and management could be particularly beneficial for soils with low organic carbon content. It's known that many of soils in the world intrinsically exhibit little ability to retain water and nutrients due to their texture and mineralogy. Also, acquiring biomass for other than agricultural purposes can reduce the organic carbon accumulation and worsens the soil quality. Adding biochar to the soil can affect saturated hydraulic conductivity, water holding capacity and reduce soil erosion and mineral fertilization. It has been shown that saturated hydraulic conductivity depends on type of feedstock and pyrolysis temperatures used for biochar production and application dose but the results are inconsistent. Therefore, in order to explain the different biochar impacts, we propose in this study the use the physical-statistical model of B. Usowicz for predicting the saturated hydraulic conductivity using literature data for various soils amended with biochars (from woodchip, rice straw and dairy manure), pyrolyzed at 300, 500 and 700 °C.  

Soil with biochar and pores between them can be represented by a pattern (net) of more or less cylindrically interconnected channels with different capillary radius. When we view a porous medium as a net of interconnected capillaries, we can apply a statistical approach for the description of the liquid or gas flow. The soil and biochar phases and their configuration is decisive for pore distribution and the course of the water retention curve in this medium. The physical-statistical model considers the pore space as the capillary net that is represented by parallel and serial connections of hydraulic resistors in the layer and between the layers, respectively. The polynomial distribution was used in this model to determine probability of the occurrence of a given capillary configuration. Capillary size radii and the probability of occurrence of a given capillary configuration were calculated based on the measured water retention curve and saturated water content. It was found a good agreement between measured and the model-predicted hydraulic conductivity data for the biochar amended soils. It indicates that the used variables and model parameters to predict the saturated hydraulic conductivities of the soils were chosen correctly. The different types and pyrolysis temperatures of biochars affected the soil water retention and the equivalent length of the capillaries that characterize the pore tortuosity in the soil.

 

Acknowledgements. Research was conducted under the project “Water in soil - satellite monitoring and improving the retention using biochar” no. BIOSTRATEG3/345940/7/NCBR/2017 which was financed by Polish National Centre for Research and Development in the framework of “Environment, agriculture and forestry” - BIOSTRATEG strategic R&D programme.

How to cite: Usowicz, B. and Lipiec, J.: Modelling the saturated hydraulic conductivity of soils amended with different biochars, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7575, https://doi.org/10.5194/egusphere-egu2020-7575, 2020.

D386 |
EGU2020-7738
Amir Golparvar, Matthias Kästner, and Martin Thullner

The vadose zone hosts a wide range of various microorganisms which provide different soil ecosystem services from nutrient cycling to biodegradation of harmful chemical substances. The efficiency of such in-situ biodegradation is influenced by different biotic and abiotic factors ranging from physical properties of the soil to the redox conditions controlled by the activity of the involved chemical compounds. One important feature of the soil system is the dynamical and simultaneous interplay of these factors, boosting or deteriorating the residing microbial community’s abundance and/or activity and hence shaping biodegradation of vadose zone contaminants. Physical properties of porous media – e.g. the pore geometry, pore size distribution, connectivity as well as the water content – play a major role in enhancing or restricting the bioavailable concentration of contaminants and other reaction partners. Pore-scale phenomena have been shown to be considerably affecting the macro-scale processes, therefore a quantitative bottom-top approach of these mechanisms in situ is adamant. Hence it is of paramount importance to understand the effect of soil physical properties on microbial activity and biodegradation of carbon compounds in soil.

Pore scale reactive transport processes have a complex, nonlinear dependency on the aforementioned factors, which severely challenges the experimental and/or numerical investigation of biodegradation at in in-situ conditions. However, the recent technological advances, specifically the imaging techniques, have made it easier to study biological and microbial evolution in porous media, but there is still a need for putting all these information together. For this purpose, numerical methods would offer the possibility of simulating a variable/controllable water saturation conditions and considering water/air dynamics and advective and diffusive micro-scale transport of all components in both, air and water phase, in porous medium structures directly obtained from CT scanned samples. Up to now, such pore-sale model approaches considering also the fate of biogeochemically reactive compounds are scarce. In this work we propose a novel reactive transport modelling technique combining the pore-scale numerical characterization of water flow and solute transport in unsaturated porous media and of biogeochemical process. For a variably saturated porous system, the presented model approach is solving the Navier Stokes equation and scalar transport equations for any arbitrary geometry and is simulating the dynamics of biogeochemical processes with any degree of complexity. Simulations are compared to experimental data to assess the effect of soil physical properties on the transport and degradation of contaminants in soil.

How to cite: Golparvar, A., Kästner, M., and Thullner, M.: A Pore-Scale Reactive Transport Model Approach for Investigating the Effect of Soil Physical Properties on Biogeochemical Processes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7738, https://doi.org/10.5194/egusphere-egu2020-7738, 2020.

D387 |
EGU2020-7887
Angelo Basile, Fabio Terribile, and Marialaura Bancheri and the LANDSUPPORT H2020 Project n.774234

Geo-Spatial Decision Support Systems (S-DSS) can be usefully employed to support the acquisition, management, and processing of both static and dynamic data (e.g., daily climate), data visualization, and computer on-the-fly applications in order to perform simulation modelling all potentially accessible via the Web. S-DSS are becoming more popular by providing operational tools to a large community of end-users and policy-makers for a sustainable landscape management (i.e. for both agriculture and environmental protection) at different spatial and temporal scales.

The scope of this work is to present the implementation of the extended Transfer Function Model (TFM-ext) – described in a companion abstract presented in the same session – as an operative tool for the groundwater vulnerability assessment within the larger S-DSS developed for LandSupport H2020 project (https://www.landsupport.eu).

The tool allows to simulate the mean travel times of a generic solute at different spatio-temporal scales (from the local to the regional scale), considering different land uses.

In particular, operatively, the end-user can evaluate the filtering capacity of the soils, by: i) defining the region of interest; ii) defining the simulation period; iii) choosing between 6 different land use scenarios (bare soil, alpha-alpha, maize, vine, olive and wheat) or consider his/her own management scenario; iv) defining the depth of interest at which evaluate the solute arrival.

The outputs are i) the mean travel times that the input solute (given as a fertilizer concentration related to the land-use scenario) takes to reach the defined depth and ii) the quantity of the input solute that reaches the defined depth after one year from its injection.

The latter information is then associated to the filtering capacity of the soil, which are thus classified according to the percentage of input mass arrived after one year.

The model was implemented as open source Java application, following the standard of the flexibility to changes and to future expansions, of the optimized computational demand and parallelization, required by the project.

Three local scale cases are available at the moment (Telesina Valley-IT, Marchfeld-AT and Zala County-HU). Future developments will aim to apply TFM-ext towards larger European spatial extent areas (e.g. regional scales). Furthermore, future develoments  will aim to support selected implementations of Water Framework and Nitrates directives, especially with respect to the systematic required mapping revision of Nitrate Vulnerable Zone and the adoption of best practice.

 

How to cite: Basile, A., Terribile, F., and Bancheri, M. and the LANDSUPPORT H2020 Project n.774234: TFM-ext tool for the groundwater vulnerability assessment within LandSupport project, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7887, https://doi.org/10.5194/egusphere-egu2020-7887, 2020.

D388 |
EGU2020-8581
Florian Heinlein, Xiaohong Duan, and Eckart Priesack

In times of climate change, many regions of the world suffer from heat waves and drought periods, which can lead to failure of crops. To a certain extent, irrigation can help to overcome these extreme events. However, in a sustainable agricultural system the water and nutrient applications should be minimized in order to avoid the waste of valuable resources.

Another method to use water more efficiently is the introduction of agroforestry systems, e.g. planting tree strips within a field. On the one hand, these tree strips reduce the evapotranspiration of the crop-soil-system due to shading and reduction of wind speed. On the other hand, temperatures tend to be higher near the trees and the tree roots may deplete available water and nutrient resources for crops.

Recently, an agroforestry sub-model has been implemented into the modular model system Expert-N to simultaneously simulate tree and crop growth. In principle, trees and crops are simulated separately at different grid points next to each other. However, the agroforestry sub-model allows for the exchange of water and matter between the different grid points to simulate mutual influences of trees and crops. Up to now the following processes are considered: shading, distribution of dead tree biomass to the crop area, and changed water distribution as tree roots grow into the crop area.

Depending on the simulated tree root length density at the crop grid points, the tree roots can uptake a certain amount of water from neighbouring grid points. If the total water demand of trees and crops cannot be fulfilled, the water uptake at the respective grid point is reduced for both, trees and crops.

Expert-N is used to simulate the plant production and the water cycle within an agroforestry system. The results comprise plant biomasses, leaf area indices, evapotranspiration, and soil water contents. To show the impact of the agroforestry sub-model on the simulation results, the differences between two simulations, which only vary in the activation of the agroforestry sub-model, are presented and discussed.

How to cite: Heinlein, F., Duan, X., and Priesack, E.: Modelling competition for water between tree and crop roots in an agroforestry system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8581, https://doi.org/10.5194/egusphere-egu2020-8581, 2020.

D389 |
EGU2020-5862
Arnaud Isch, Carlos Aldana, Yves Coquet, and Mohamed Azaroual

Water retention and hydraulic conductivity are the most important properties governing water flow and solute transport in unsaturated porous media. However, transport processes in the vadose zone (VZ) are still not completely understood, in spite of their importance for the preservation and management of aquifers, especially in the geographic zones under intensive agriculture. This study has been carried out as part of the construction of the O-ZNS platform (Observatory of transfers in the vadose zone). This platform aims to integrate observations over a wide range of spatial and temporal scales thanks to a large access well (depth–20 m & diameter–4m) surrounded by several boreholes in order to combine broad characterization and focused monitoring techniques.

Three cored boreholes have been drilled in Spring 2017. Structural and mineralogical analyses were carried out for four types of materials sampled throughout the entire VZ profile (20 m depth) including soft sediments (soil, marl and sand) and fractured limestone rock. Hydraulic properties (q(h) and K(h)) were measured on representative core samples by means of a triaxial system used by applying the multistep outflow method. Simulations were then made using HYDRUS-1D to simulate water flow and bromide (conservative tracer) transport over 50 years using meteorological and water table level data.

The results brought valuable information about factors contributing to the heterogeneity of hydraulic properties within the VZ. For the applied matric heads (from 0 to -1000 cm), the water content and hydraulic conductivity of (i) the soft materials (9 samples) ranged from 0.173 to 0.485 cm3/cm3 and from 1.26.10-5 to 2.41 cm/d, respectively ; (ii) the hard materials (5 samples) ranged from 0.063 to 0.340 cm3/cm3 and from 8.54.10-5 to 1.82 cm/d, respectively. The shape of the water retention and hydraulic conductivity curves obtained for the soft sediments is strongly related to the physical properties of the material but also to the proportion and the nature of clay minerals. The soil material displayed the largest average water retention capacity due to the presence of smectite and kaolinite, indicating weathering and matrix transformation. The water retention capacity of the marl and sand materials was lower due to higher content in palygorskyte and calcite. The limestone rock materials displayed an important heterogeneity in their hydraulic properties. Mineralogical analysis helped understanding water flow pathways within the limestone aquifer. The non-altered matrix, that seemed impermeable at first sight, presented few thin microfractures where water probably accumulates. The altered matrix showed microfractures where water has circulated and calcite has been replaced by phyllosilicates, thus increasing the water retention capacity. Natura macrofractures observed at dm-scale showed the presence of iron oxides which highlighted an exposure to high water flow. Simulations made using HYDRUS-1D allowed a first estimation of water and solutes travel time through this highly heterogeneous vadose zone. The results highlighted transfer time of between 25 to 35 years for the bromide to reach water table. The differences observed between the three cored boreholes were mainly due to the heterogeneity of the marl materials located between 1 and 7 m deep.

How to cite: Isch, A., Aldana, C., Coquet, Y., and Azaroual, M.: Material Characteristics, Hydraulic Properties, and Water Travel Time through the Heterogeneous Vadose Zone of a Cenozoic Limestone Aquifer (Beauce, France), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5862, https://doi.org/10.5194/egusphere-egu2020-5862, 2020.

D390 |
EGU2020-8716
Eckart Priesack, Xiaohong Duan, Sebastian Gayler, and Florian Heinlein

We present an example for the generation of model ensembles by use of the model framework Expert-N. Different crop models are obtained by choosing different sub-models, which represent important processes to determine the dynamics of crop growth. In this way, different sub-models to simulate potential evapotranspiration, actual evaporation, actual transpiration, soil water flow, soil nitrogen transport, soil carbon and nitrogen turnover, crop development, canopy photosynthesis, potential and actual nitrogen uptake and crop growth are combined resulting in different crop models building a model ensemble. The sub-models are based on process descriptions that are included in the crop models CERES, SUCROS, SPASS and GECROS, but also stem from known soil models such as CENTURY, SOIL, SOILN, NCSOIL, LEACHM or HYDRUS.

The generated model ensemble is applied to simulate winter wheat growth at a field site in Southern Germany. We compare simulation results to measurements of crop biomasses and yields, and to soil water and nitrogen contents. It is concluded that model frameworks as the model system Expert-N can help to analyse structural uncertainties which lead to different simulation results between models of a model ensemble.

How to cite: Priesack, E., Duan, X., Gayler, S., and Heinlein, F.: Multi-Model Ensemble Crop Growth Simulation by use of the model framework Expert-N, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8716, https://doi.org/10.5194/egusphere-egu2020-8716, 2020.

D391 |
EGU2020-11240
Jean-Michel Pereira and Patrick Dangla

The definition of a suitable effective stress to model the behaviour of unsaturated soils has been questioned for decades. This issue is still a matter of debate in the community. Recently, Alonso et al. (2010) have shown that this coefficient might depend on the microstructure of the soil and that fine plastic soils are characterised by a Bishop coefficient tending to deviate from the commonly used assumption according to which it is equal to the degree of saturation. On the other hand, Coussy et al. (2010) have shown that this coefficient deviates from the latter assumption if the isodeformation of all pores is not satisfied. They also showed that the Bishop coefficient might be different in elastic and plastic regimes, respectively.

In this work, we take advantage of experimental data available in the literature covering, for each soil, both elastic and plastic regimes at various saturation states and including the water retention curve together with microstructure data. We conclude that the Bishop coefficient depends on the deformation regime and that, in particular, distinct values might be used depending whether the plastic regime is active or not.

References:

Alonso, E. E., Pereira, J. M., Vaunat, J., & Olivella, S. (2010). A microstructurally based effective stress for unsaturated soils. Géotechnique, 60(12), 913–925. https://doi.org/10.1680/geot.8.P.002

Coussy, O., Pereira, J. M., & Vaunat, J. (2010). Revisiting the thermodynamics of hardening plasticity for unsaturated soils. Computers and Geotechnics, 37(1–2), 207–215. https://doi.org/10.1016/j.compgeo.2009.09.003

How to cite: Pereira, J.-M. and Dangla, P.: Bishop coefficients in elastic and plastic regimes of unsaturated soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11240, https://doi.org/10.5194/egusphere-egu2020-11240, 2020.

D392 |
EGU2020-12881
Tomas Vogel, Michal Dohnal, Jana Votrubova, and Jaromir Dusek

Increasingly, numerical models of varying complexity are used to simulate the thermal and water balance of soils exposed to freezing-thawing cycles. An important aspect of soil freezing modeling is the highly non-linear nature of the energy balance equation during phase transition. To handle the transformation between sensible and latent heat during freezing–thawing events, the majority of existing models employ the concept of apparent heat capacity. The main disadvantage of this approach is that the apparent heat capacity increases by several orders of magnitude at the freezing point, which complicates the numerical solution, possibly causing numerical oscillations and convergence problems.

An alternative approach was developed to facilitate the simulations of soil water flow and energy transport during sporadic freezing–thawing episodes, which are typical for the winter regime of humid temperate continental climate. The approach is based on an accurate non-iterative algorithm for solving highly non-linear energy balance equation during phase transitions. The suggested modeling approach abstracts from many complexities associated with the freezing phenomena in soils, yet preserves the principal physical mechanism of conserving the internal energy of the soil system during the phase transitions. When applied to simulate occasional freezing soil conditions, the model algorithm delivers the desired effect of slowing down the propagation of surface freezing temperatures into deeper soil horizons by converting water latent heat into sensible heat. The model also allows the evaluation of the extent and duration of frozen soil conditions – a crucial information for soil water flow modeling, as the frozen soil significantly reduces the soil hydraulic conductivity.

The proposed algorithm was successfully verified against analytical solutions for idealized freezing and thawing conditions and applied to both hypothetical and real field conditions.

How to cite: Vogel, T., Dohnal, M., Votrubova, J., and Dusek, J.: Non-iterative numerical model of soil freezing, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12881, https://doi.org/10.5194/egusphere-egu2020-12881, 2020.

D393 |
EGU2020-15351
Juliana Arbelaez Gaviria and Michal Kuraz

Evaporation is a dynamic and nonlinear process that incorporates various internal transport mechanisms which is important in the unsaturated zone in arid regions under low soil moisture conditions [1, 2]. The governing equations are formed out of the coupled Richards equation with the heat transport equation, where the boundary conditions originate from the surface energy balance. The purpose of this contribution is to present a numerical model simulating coupled water and heat flow in a porous medium with phase changes due to evaporation. The nonlinear nature of this problem, which originates both from the nonlinear Richards equation and latent heat exchange, which in turn governs the heat gradient, requires a proper temporal discretization in order to maintain numerical solution of sufficient qualities. The net evaporation rate is temperature and water content dependent, where the heat transferred downward by thermal conduction into the soil when the soil surface is warming by solar radiation or conducted back to the surface when the temperature of the top of the soil cools. Evaporation rates from terrestrial surfaces are very common to quantify in terms of energy flow leaving the evaporating surface as latent heat of vaporization of the water vapor. In this contribution, it is presented a numerical implementation of this coupled dynamic process and describes the computational difficulties which arise from this nonlinear process, including a numerical comparison between the common approach for evaluating evaporation in soils by using the Penman-Monteith [3] equation and the coupled water and heat flow modeling approach.

References

[1] Hirotaka Saito, Jiri Simunek, and Binayak P Mohanty. Numerical analysis of coupled water, vapor, and heat transport in the vadose zone. Vadose Zone Journal, 5(2):784–800, 2006.

[2]  Masaru Sakai, Scott B Jones, and Markus Tuller. Numerical evaluation of subsurface soil water evaporation derived from sensible heat balance. Water Resources Research, 47(2), 2011.

[3]  Richard G Allen, Luis S Pereira, Dirk Raes, Martin Smith, et al. Crop evapotranspiration-guidelines for computing crop water requirements-fao irrigation and drainage paper 56. Fao, Rome, 300(9):D05109, 1998.

How to cite: Arbelaez Gaviria, J. and Kuraz, M.: Numerical solution analysis of water flow in porous medium under phase changes due to evaporation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15351, https://doi.org/10.5194/egusphere-egu2020-15351, 2020.

D394 |
EGU2020-16036
Johanna Blöcher and Michal Kuraz

The freezing process in soils is important in many natural systems and, consequently, it is of great interest to model it accurately. 
The freezing of water in soil is coupled to the heat equation as freezing releases latent heat and temperature is an important variable that determines whether water is in solid or liquid state. In soils, water can remain liquid under sub-zero temperatures (freezing-point depression). This effect is often modeled with the Clapeyron equation. With the Clapeyron equation, a temperature dependent pressure head definition for the total water content (liquid + frozen water) and the liquid water can be derived. When the temperature of the soil system falls below the freezing point, the system switches between the pressure head definitions. However, this switch can cause a discontinuity at the freezing front leading to numerical issues and unrealistic results.

To compensate for the discontinuity, we discuss the use of regularisation of the switching term on, both, synthetic and experimental data of case studies of freezing column experiments. 

How to cite: Blöcher, J. and Kuraz, M.: The issue of switching between non-freezing and freezing in soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16036, https://doi.org/10.5194/egusphere-egu2020-16036, 2020.

D395 |
EGU2020-17910
Teodolina Lopez, Haijun Hu, Yujun Cui, Raphaël Antoine, and Ni An

The 49,000-km2 Badain Jaran Desert lies in the centre of Alxa Plateau in the western Inner Mongolian Region [1;2]. The southern part of this desert is characterised by the unique association of lakes with the tallest megadunes of Earth (general height varying between 150 and 350 m). The mean precipitation rate of this region is below 100 mm yr-1 and the evapotranspiration one is ~2600 mm yr-1. Around 140 lakes have been reported, mainly located in the interdunal region and they represent a mean surface of ~23 km2. In order to protect the water resource of this desert, scientific research such as the sources of groundwater and groundwater recharge has been carried out. One of the most interesting resulting hypotheses is the existence of a convective circulation of the groundwater [3;4;1;5]. Indeed, the ascending current of groundwater can 1) supply the lakes and 2) may play role in the cementation of the megadunes, process that is considered as the starting point for their development. Interestingly, at the surface of the megadunes, a dry layer is present and its depth varies between 20 and 50 cm. But below this dry layer, the sand is moistened [6].

Space-based thermal images from MODIS of this region display at first approximation a correlation between the topography and the surface temperature evolution. In order to understand the relationship between the surface temperature, topography and soil moisture, a fully coupled hydro-thermal method was adopted to simulate the interaction between the atmosphere and the first metre below the surface. The analysis process includes the determination of material parameters, initial and boundary conditions, the calculations of net solar radiation, actual evaporation and sensible heat. Our methodology relies on the measured temperature distribution by MODIS and the calculation shows the temperature evolution along with the elevation. The factors including sunshine direction (i.e. sunny or shadowed slope) and evaporation on the surface temperature distribution at Badain Jaran will be discussed.

[1] Dong et al. (2004), Geomorphology, doi: 10.1016/j.geomorph.2003.07.023; [2] Dong et al. (2009), Geomorphology, doi: 10.1016/j.geomorph.2008.10.015; [3] Chen et al. (2004), Nature, doi: 10.1038/432459a; [4] Chen et al. (2012), Geochemistry International, doi: 10.1134/s0016702912030044 ; [5] Gates et al. (2008), Applied Geochemistry, doi: 10.1016/j.apgeochem.2008.07.019; [6]  Chen et al. (2006), Chinese Science Bulletin, doi; 10.1007/s11434-006-2196-8

How to cite: Lopez, T., Hu, H., Cui, Y., Antoine, R., and An, N.: Analysis of the space-based surface temperature distribution in Badain Jaran Desert, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17910, https://doi.org/10.5194/egusphere-egu2020-17910, 2020.

D396 |
EGU2020-19586
Kim Schwartz Madsen, Bo Vangsø Iversen, and Christen Duus Børgesen

Modelling is often used to acquire information on water and nutrient fluxes within and out of the root zone. The models require detailed information on the spatial variability of soil hydraulic properties derived from soil texture and other soil characteristics using pedotransfer functions (PTFs). Soil texture can vary considerably within a field and is cumbersome and expensive to map in details using traditionally measurements in the laboratory. The electrical conductivity (EC) of the soil have shown to correlate with its textural composition.

This study investigates the ability of electromagnetic induction (EMI) methods to predict clay content in three soil layers of the root zone. As the clay fraction often is a main predictor in PTFs predicting soil hydraulic properties this parameter is of high interest. EMI and soil textural surveys on four Danish agricultural fields with varying textural composition were used. Sampling density varied between 0.5 and 38 points per hectare. The EMI data was gathered with a Dualem21 instrument with a sampling density 200-3000 points per hectare. The EC values were used together with the measured values of the clay content creating a statistical relationship between the two variables. Co-kriging of the clay content from the textural sampling points with the EC as auxiliary variable produces clay content maps of the fields. Unused (80%) texture points were used for validation. EMI-predicted clay content maps and clay content maps based on the survey were compared. The two sets of soil texture maps are used as predictors for PTF models to predict soil hydraulic properties as input in field-scale root zone modelling.

The comparisons between EC and clay content show some degree of correlation with an R2 in the range of 0.55 to 0.80 for the four fields. The field with the highest average clay content showed the best relationship between the two parameters. Co-kriging with EC decreased mean error by 0.016 to 0.52 and RMSE by 0.04 to 1.80 between observed and predicted clay maps.

How to cite: Madsen, K. S., Iversen, B. V., and Børgesen, C. D.: Geophysical mapping of soil texture variability in the root zone to improve modelling of the water and nutrient flow., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19586, https://doi.org/10.5194/egusphere-egu2020-19586, 2020.

D397 |
EGU2020-21112
Ryan Stewart and Jesse Radolinski

Many soil physical models assume a homogeneous domain and equilibrium conditions, even as decades of evidence have suggested that such states are rarely present in the real world. Instead, natural soils tend to be characterized by physical heterogeneity (e.g., macropores) and non-equilibrium movement of water, solutes and gases (e.g., preferential flow and transport), making it critical to develop physically realistic yet parsimonious descriptors of these processes. In this presentation we discuss recent advances using multi-domain descriptions of soils to model preferential flow and subsurface contaminant movement under field conditions. Here we emphasize the use of simplifying assumptions and straightforward parameterizations, and consider whether those factors constrain the ability of such models to realistically represent underlying physical mechanisms. We also discuss results of an innovative field experiment aimed at constraining macropore porosity, which is a key yet highly uncertain factor in such multi-domain models. Finally, we consider the relevant scales of these multi-domain models, and whether such approaches merit consideration in larger (e.g., hillslope- or catchment-scale) simulations.    

How to cite: Stewart, R. and Radolinski, J.: It’s a macroporous world; we just model in it, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21112, https://doi.org/10.5194/egusphere-egu2020-21112, 2020.

D398 |
EGU2020-22342
Julian Krause, Christian Schäfer, Birgit Terhorst, Roland Baumhauer, and Heiko Paeth

This research is part of the integrated project “BigData@Geo - Advanced Environmental Technology Using AI In The Web” funded by the European Regional Development Fund (ERDF). The aim of this ERDF-project is to develop a high-resolution regional earth system model for the region of Lower Franconia. One sub-project is dedicated to regional soil moisture modelling created with WaSiM-ETH based on soil moisture monitoring data. The second sub-project aims to improve the resolution of the regional climate model REMO. Both models will be combined to form the earth system model.

Lower Franconia is amongst the regions in Germany, which will be strongly affected by climate change. Regional climate models show that average temperatures will rise and dry periods as well as extreme precipitation events occur more often. However, it is still not known, what effect the changing climate conditions – especially dry periods and extreme precipitation events – will have on the soils in Lower Franconia.

Yields of forestry and agriculture (including viticulture and pomiculture) depend very much on the availability of soil water. During the growing season the water retention capacity of soils is therefore highly relevant. Up to present, datasets as well as modelling results of future scenarios on soil moisture are only scarcely available on local as well as on regional scale. In order to generate future scenarios, calculation of the soil moisture regime forms the base in order to evaluate present day conditions as well as to develop prognostic studies. As we intend to obtain most realistic parameters, generation of real-time data with high temporal resolution at selected sites is crucial. They are characteristic for Lower Franconia serving as calibration regions for modelling approaches. The operating monitoring stations record soil moisture and - temperature as well as meteorological parameters.

In order to obtain data on dynamics and causes of soil moisture fluctuation as well as to understand process flows, soil geographical surveys form an essential component of our research design for selected sites related to the monitoring stations. Furthermore, relevant sedimentological and pedological parameters such as grain size distribution, permeability, and bulk density are analyzed in the laboratory. Thus, our representative test sites combine detailed ground-truth data combining soil moisture and soil quality and thus, form consecutive modules as parts of soil moisture models. These modules drive and control the modelling procedures of the sub-project and they further serve for assessment and calibration of the area-wide hydrological and climate modelling in the “BigData@Geo” ERDF-project.

How to cite: Krause, J., Schäfer, C., Terhorst, B., Baumhauer, R., and Paeth, H.: Monitoring and Modelling of Soil Moisture in Lower Franconia (Germany), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22342, https://doi.org/10.5194/egusphere-egu2020-22342, 2020.